It is often desirable or necessary to retain equipment components without threading, piercing or otherwise re-working one of the components. Securing ceramic magnets in a steel housing ring for permanent magnet motors is one example. Spring retainer clips and adhesives are common means for accomplishing this objective.
Adhesive techniques and materials offer a wide variety of approaches for securing articles to one another. However, there are inherent disadvantages including the time required and the special equipment needed for curing the adhesive; the handling, mixing, applying, and cleaning up of the adhesive; and precautions against noxious or toxic effects. Further, the costs of special quick-drying adhesives and related special equipment, and the troubles of maintaining the necessary tight control of surface tolerances are often significant. To avoid these, sometimes assemblies are secured with the use of both an adhesive and retainer clips. The retainer clips may be removed after the adhesive has set, or they may be left in permanently, depending upon individual economic and structural considerations.
The use of spring retainers in lieu of adhesives is desirable, where practical. In some cases, the spring retainers--typically bow or wave-shaped flat metal compression springs--are pressed or snapped into their final loaded position. In other applications the springs and magnets are assembled loosely in a larger diameter fixture, after which the assembly is compressed radially, and then axially inserted into the cylindrical housing.
There are a number of problems which limit the use and effectiveness of the existing spring retainer approaches. Variations in the arc lengths of the articles to be retained, and in dimensions of other mating components, pose difficulties with respect to critical relationships between the retainer spring's relatively short length, and the requirements for both sizeable loads and large tolerance take-up capabilities. Closer control of tolerances entails higher costs. Also, the pre-compression, as well as the snap-in assembly operations often tend to break or chip ceramic magnets or other brittle articles. In some instances, spring retention systems have been avoided and even abandoned because of concern for unacceptable breakage, or for displacement from impacts during assembly, handling, shipping or use.
The need remains for a basically improved mechanical retention system which is adaptable to:
a. large tolerance variations beyond the working length of ordinary springs; PA1 b. providing sizeable, and consistent holding forces without damaging magnets or other parts being retained; and PA1 c. easy and rapid manual or automatic assembly techniques (without contending with spring loads during assembly of components). The term "working" is sometimes used to describe the spring of this invention. It is in fact a spring which continues to exert a bias force adaptable both in compression and extension. The application of this force as retention means is merely one application, in which it resists cyclical vibratory forces and thermal expansion and compression as encountered in electrical motors, while still pressing against an article such as a magnet to hold it in place. Its movements are similar to those of an actuator.